1. Field of the Invention
The present invention relates to a system and a method for fabricating a semiconductor device, and more particularly to a system and a method for drying a semiconductor substrate.
2. Description of the Related Art
In fabricating highly integrated semiconductor devices, any contamination materials such as particles remaining on semiconductor substrates after cleaning, electrostatic discharge, and water marks or the like, exert an undesirable influence on subsequent process steps and adversely affect device yield. Generally, semiconductor devices are cleaned during fabrication by a wet cleaning process or wet etching process to remove contaminants from semiconductor substrates. After a wet cleaning process, a cleaning process generally is used to remove chemical solution used in the wet process from semiconductor substrates, and a drying process is used to remove fluid such as deionized water used in the cleaning process from the rinsed semiconductor substrates.
Several conventional methods are used to dry the semiconductor substrates, for example, drying by spinning the substrates or by using vapor pressure. The spin drying method spins the substrates and fluid is removed by centrifugal force. The spin drying method has problems in that the semiconductor substrates may break due to the high level of mechanical force exerted on the semiconductor substrates. Further, this process often does not sufficiently dry the semiconductor substrates.
The vapor pressure method generally involves use of isopropyl alcohol (IPA) at low pressure. In addition to pressure, use of the Marangoni principle further dries the substrates. The process holds the fluid flow from lower to higher surface tension regions across a fluid surface to maximize the drying efficiency.
A method and apparatus for drying semiconductor substrates using the Marangoni principle is disclosed in U.S. Pat. No. 5,884,640 and Japanese Patent Laid-Open No. 10-335299. In these proposed methods, fluid is supplied to a bath by flow onto the top surface of the bath and the bath is drained from the bottom through a valve. Vapor is supplied from a gas supply through a plurality of openings adjacent to the bath. Disadvantages of these methods include fluid surface turbulence, i.e., as fluid is flowed onto the fluid surface level, the fluid is disturbed. This causes an uneven drying effect. Thus, drying efficiency of semiconductor substrates using the Marangoni principle may be reduced because uniform meniscus may not be formed on the surface of the substrates during the drying process. Also the fluid level control disclosed may not be capable of providing a continuous fluid supply and drainage. Further, vapor zone above the fluid level in the drying chamber has inadequate spacing to allow uniform distribution of the vapor pressure of isopropyl alcohol. Furthermore, as the fluid and the vapor are recycled, contaminants may be present.
Therefore, it is desirable to have a system and a method for drying semiconductor substrates for uniformly distributing drying gas and stabilizing fluid surface level in a drying chamber, thereby enhancing the Marangoni effect.
A drying system for drying a semiconductor substrate is provided, which includes: a chamber for housing a vapor distributor and a fluid bath, said fluid bath being disposed in a lower portion of the chamber and said distributor being disposed in an upper portion of the chamber for distributing vapor for drying the substrate; and a fluid flow system for supplying fluid flow into said fluid bath for cleaning and drying the substrate and for draining said fluid from the fluid bath, wherein the chamber includes a plurality of exhaust vents disposed at the upper portion for venting the vapor.
According to an embodiment of the present invention, the plurality of exhaust vents preferably include at least one pair of exhaust vents disposed substantially diametrically opposed to each other. The fluid flow system controls fluid flow and drain in combination with the vapor distributor to effect the Marangoni drying principles. The fluid flow system includes a fluid level controller for adjusting the level of and draining the fluid in said fluid bath, said fluid level controller having means for continuously draining and supplying the fluid from and to said fluid bath during the drying process. The means for continuously draining includes a flex conduit connected to a drain of said fluid bath, and the level of fluid in the fluid bath is adjusted by raising or lowering a portion of the flex conduit.
According to an embodiment of the present invention, the fluid flow system includes a fluid flow buffer for receiving and buffering fluid flow into the fluid bath. The flow buffer is disposed at an upper portion of the fluid bath, said flow buffer being sized and shaped to receive the fluid at an upper portion and release the fluid through a slit at a lower portion. And the fluid flow buffer is disposed at an upper portion of the fluid bath, said flow buffer being sized and shaped to receive the fluid at an upper portion, temporarily hold the fluid, and release the fluid to the fluid bath by overflowing at the upper portion.
According to an embodiment of the present invention, the vapor distributor includes an inner conduit and a coaxial outer conduit, said inner conduit having an open end and a closed end, the open end for receiving vapor flow, said inner conduit having a plurality of uniformly spaced holes aligned along a longitudinal axis for passing the vapor flow received at the open end to the coaxial outer conduit, and said coaxial outer conduit having first and second sets of holes, the first set of holes aligned along a first longitudinal axis and the second set of holes aligned along a second longitudinal axis for passing the vapor flow passed from the inner conduit. First and second longitudinal axes are preferably symmetrical to each other with respect to a vertical axis passing through the center of the inner conduit.
According to an embodiment of the present invention, the drying system further includes a guide disposed beneath the distributor, the guide being sized to have a width smaller than the diameter of the chamber, forming a channel between the guide and the sides of the chamber to pass the vapor from the distributor. The guide includes a bottom surface formed by two sloped sides intersecting at the middle for reflecting the vapor from the channel to the fluid bath.
According to an embodiment of the present invention, the drying system further includes a vapor generator for generating vapor, said vapor generator having an expansion tank, said expansion tank having a heating element for heating a mist and a filter for filtering the mist prior to outputting as vapor to the chamber.
According to an embodiment of the present invention, the drying system further includes a vapor generator for generating vapor, said vapor generator having an expansion tank, a carrier gas conduit, and a nozzle connecting the carrier gas conduit and the expansion tank, said nozzle having a constant diameter therethrough.
According to a preferred embodiment of the present invention, the chamber includes a hood connecting a top cover and the fluid bath, the plurality of exhaust vents being disposed adjacent a top of the hood. The distance between the fluid surface level and the top cover is at least a half diameter of the semiconductor substrate in height.
According to an embodiment of the present invention, the drying system further includes a plurality of bars for retaining the substrate in the fluid bath, said plurality of bars being connected to a controller for selectively raising and lowering the plurality of bars and the substrate in the fluid bath.
According to an embodiment of the present invention, the fluid is deionized water and said vapor includes isopropyl alcohol.
A method of drying a semiconductor substrate is also provide, which includes the steps of: housing in a chamber having a first space and a second space a vapor distributor in the first space and a fluid bath in the second space, said first space and said second space being spatially separated by a hood; and supplying fluid flow into said fluid bath for cleaning and drying the substrate; drying said substrate by mixing vapor injected from said distributor with fluid in said fluid bath and continuously draining fluid from and supplying fluid to the fluid bath.
According to an embodiment of the present invention, the step of drying includes exhausting vapor through exhaust vents disposed at the hood adjacent said first space. The method further includes the step of adjusting the level of fluid in said fluid bath by raising or lowering a portion of a flex conduit connected to a drain of the fluid bath. The method further includes the step of lowering the level of fluid in said fluid bath by lowering a portion of a flex conduit connected to a drain of the fluid bath and raising said substrate in the fluid bath concurrently. The method further includes the step of buffering fluid flow into the fluid bath by a fluid flow buffer.